Exhibit 5.1

[COOLEY GODWARD LETTERHEAD]

May 3, 2002

IXYS Corporation
3540 Bassett Street
Santa Clara, California 95054-2704

Ladies and Gentlemen:

We have acted as counsel for IXYS Corporation, a Delaware corporation (the
"Company"), in connection with the merger (the "Merger") and other transactions
contemplated by that certain Agreement and Plan of Merger and Reorganization,
dated as of April 22, 2002, by and among the Company, Teacup Acquisition Corp.,
a Massachusetts corporation and a wholly-owned subsidiary of the Company, and
Clare, Inc., a Massachusetts corporation. This opinion is being furnished in
connection with a Registration Statement on Form S-4 (the "Registration
Statement"), to be filed by the Company with the Securities and Exchange
Commission covering the offer and sale of up to 5,908,973 shares of the
Company's common stock, $0.01 par value per share (the "Common Stock"), to be
issued in connection with the Merger.

In rendering this opinion, we have examined the following documents: (i) the
Company's Amended and Restated Certificate of Incorporation and Bylaws, (ii) the
resolutions adopted by the Board of Directors of the Company on April 22, 2002,
(iii) the Registration Statement, and (iv) such other documents, legal opinions
and precedents, corporate and other records of the Company and certificates of
public officials and officers of the Company that we have deemed necessary or
appropriate to provide a basis for the below opinion.

Based upon and subject to the foregoing, in our opinion, the shares of Common
Stock of the Company which are being offered and sold by the Company pursuant to
the Registration Statement, when sold in the manner and for the consideration
contemplated by the Registration Statement, will be validly issued, fully paid
and non-assessable.

We consent to the filing of this opinion as an Exhibit to the Registration
Statement and to the reference to our firm under the heading "Legal Matters."

Very truly yours,

Cooley Godward LLP


By: /s/ SUZANNE SAWOCHKA HOOPER
    ---------------------------
Suzanne Sawochka Hooper